Multizone convection furnaces are employed for a variety of thermal processing applications such as reflow soldering of components on a printed circuit board and sintering of ceramic multilayer circuits or other ceramic objects. Convection furnaces by their nature move very large volumes of gas in a recirculating path within independently thermally controlled zones. It is difficult to prevent the mixing of gas between adjacent zones that are operating at different temperatures. The gas in the higher temperature zone tends to move to the adjacent lower temperature zone causing the temperature in the lower temperature zone to become hotter than intended. As a result, the specified temperature profile is difficult to maintain and requires more critical adjustment in an effort to maintain the intended profile.